Don't get me wrong, I really have a healthy respect for and no fear of snakes-poisonous or not. I love to handle the ones I encounter in the wild (if they have the right disposition..) and I appreciate their beauty and unique place in our ecosystem. Definitely one on God's marvelous creatures. That said, the practice of using them in worship seems to come from a misunderstanding of the verse. Take the apostle Paul for instance; as recorded in Acts 28 was bitten by a serpent while gathering some wood for a fire. The fact that he didn't die amazed those watching for him to soon collapse and was "a sign" that he was being protected by God. He did not go out and find snakes or intentionally drink poison to prove to anyone that he had God's favor.
@Dwight Notgiving I totally agree.